Electrostatic spray device provided with electric-arc protection means

Abstract

An electronic safety device to prevent electrical arcing in electrostatic sprayer apparatus for spraying material such as paint comprises a device for generating a very low voltage AC signal in a fixed supply and control unit and a voltage step-up device in a mobile sprayer. A device sensitive to variations in the alternating current flowing in the conductors linking the generating device to the step-up device is connected to a disabling device capable, for example, of blocking the generating device when too sudden a current variation is measured, since such a current variation may precede electrical arcing.

We claim: 
     
       1. Electrostatic sprayer apparatus comprising means for generating a low voltage AC signal and means for stepping up said voltage of said Ac signal, means for sensing variations in the alternating current flowing between said generating means and said stepping up means , and means for disabling said generating means, said disabling means being controlled by said means for sensing current variations. 
     
     
       2. Apparatus according to claim 1, wherein said means for sensing variations in the alternating current comprise means for sensing said current coupled to a circuit linking said signal generating means to said stepping up means, means for generating a signal representative of the value of said current, and differentiating means connected to said current sensing means, said differentiating means comprising means for receiving said representative signal. 
     
     
       3. Apparatus according to claim 2, further comprising rectifying means connected to an output of said differentiating means and a comparator , said comparator including a first input which is connected to an output of said rectifying means and a second input which is linked to means for generating a reference voltage. 
     
     
       4. Apparatus according to claim 3, wherein said rectifying means comprise rectifier-level adapter means including two legs connected in parallel, said legs respectively transmitting positive and negative pulses from said differentiating means at different rates of amplification. 
     
     
       5. Apparatus according to claim 4, wherein said means for sensing said current comprises a resistor inserted in series in a conductor linking said AC signal generating means to said stepping up means, and a rectifier circuit connected to terminals of said resistor. 
     
     
       6. Apparatus according to claim 3, wherein said means for sensing said current comprise a resistor inserted in series in a conductor for linking said AC signal generating means to said stepping up means, and a rectifier circuit connected to terminals of said resistor. 
     
     
       7. Apparatus according to claim 1, wherein said disabling means are linked to a blocking input of a chopper-oscillator or similar device in said AC signal generating means. 
     
     
       8. Apparatus according to claim 1, wherein said disabling means are connected to means for controlling grounding of the output of said means for stepping up said AC signal voltage. 
     
     
       9. An electrostatic sprayer apparatus comprising means for generating a low voltage AC signal and means for stepping up said voltage of said AC signal, means for sensing variations in the alternating current flowing between said generating means and said stepping up means, and means for disabling said generating means, said disabling means being controlled by said means for sensing current variations, wherein said means for sensing variations in the alternating current comprise means for sensing said current coupled to a circuit linking said generating means to said stepping up means, means for generating a signal representative of the value of said current, and differentiating means connected to said current sensing means for receiving said representative signal, and further comprising rectifying means connected to an output of said differentiating means and a comparator, said comparator including a first input which is connected to an output of said rectifying means and a second input which is linked to means of generating a reference voltage, wherein said rectifying means comprise rectifier-level adaptor means including two legs connected in parallel, said legs respectively transmitting positive and negative pulses from said differentiating means at different rates of amplification. 
     
     
       10. Electrostatic sprayer apparatus comprising means for generating a low voltage AC signal and means for stepping up said AC signal voltage, said AC signal generating means supplying voltage through at least one long electric cable from a base unit to a mobile unit in which said stepping up means is located, said apparatus further comprising means for sensing variations in alternating current flowing in said long electric cables between said generating means and said stepping up means, and further comprising means for disabling said generating means, said disabling means being controlled by said means for sensing said current variations, said sensing means being located in said base unit.